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MDL-29520 question engine: work-around bad MySQL delete performance.

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This is a temporary fix, until the new API from MDL-29589 is available.

(amended to fix comments)
This commit is contained in:
Tim Hunt
2011-10-04 12:03:41 +02:00
committed by Eloy Lafuente (stronk7)
parent 7042a252c5
commit f0bfd964ba
1 changed files with 44 additions and 0 deletions
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question/engine/datalib.php
+44
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@@ -659,6 +659,11 @@ ORDER BY
WHERE $where)", $params);
}
if ($this->db->get_dbfamily() == 'mysql') {
$this->delete_usage_records_for_mysql($qubaids);
return;
}
$this->db->delete_records_select('question_attempt_step_data', "attemptstepid IN (
SELECT qas.id
FROM {question_attempts} qa
@@ -678,6 +683,40 @@ ORDER BY
"{question_usages}.id {$qubaids->usage_id_in()}", $qubaids->usage_id_in_params());
}
/**
* This function is a work-around for poor MySQL performance with
* DELETE FROM x WHERE id IN (SELECT ...). We have to use a non-standard
* syntax to get good performance. See MDL-29520.
* @param qubaid_condition $qubaids identifies which question useages to delete.
*/
protected function delete_usage_records_for_mysql(qubaid_condition $qubaids) {
// TODO once MDL-29589 is fixed, eliminate this method, and instead use the new $DB API.
$this->db->execute('
DELETE qu, qa, qas, qasd
FROM {question_usages} qu
JOIN {question_attempts} qa ON qa.questionusageid = qu.id
JOIN {question_attempt_steps} qas ON qas.questionattemptid = qa.id
JOIN {question_attempt_step_data} qasd ON qasd.attemptstepid = qas.id
WHERE qu.id ' . $qubaids->usage_id_in(),
$qubaids->usage_id_in_params());
}
/**
* This function is a work-around for poor MySQL performance with
* DELETE FROM x WHERE id IN (SELECT ...). We have to use a non-standard
* syntax to get good performance. See MDL-29520.
* @param string $test sql fragment.
* @param array $params used by $test.
*/
protected function delete_attempt_steps_for_mysql($test, $params) {
// TODO once MDL-29589 is fixed, eliminate this method, and instead use the new $DB API.
$this->db->execute('
DELETE qas, qasd
FROM {question_attempt_steps} qas
JOIN {question_attempt_step_data} qasd ON qasd.attemptstepid = qas.id
WHERE qas.questionattemptid ' . $test, $params);
}
/**
* Delete all the steps for a question attempt.
* @param int $qaids question_attempt id.
@@ -693,6 +732,11 @@ ORDER BY
FROM {question_attempt_steps}
WHERE questionattemptid $test)", $params);
if ($this->db->get_dbfamily() == 'mysql') {
$this->delete_attempt_steps_for_mysql($test, $params);
return;
}
$this->db->delete_records_select('question_attempt_step_data', "attemptstepid IN (
SELECT qas.id
FROM {question_attempt_steps} qas